Kondo Breakdown as a Selective Mott Transition in the Anderson Lattice

We show within the slave boson technique, that the Anderson lattice model exhibits a Kondo breakdown quantum critical point (KB-QCP) where the hybridization goes to zero at zero temper- ature. At this fixed point, the f-electrons experience as well a selective Mott transition separating a local-moment phase from a Kondo-screened phase. The presence of a multi-scale QCP in the An- derson lattice in the absence of magnetism is discussed in the context of heavy fermion compounds. This study is the first evidence for a selective Mott transition in the Anderson lattice.Comment: 4 pages, 2 figures, version with new figures and typos correcte

Critical phenomena near the antiferromagnetic quantum critical point of Heavy-Fermions

We present a study of the critical phenomena around the quantum critical point in heavy-fermion systems. In the framework of the S=1/2 Kondo lattice model, we introduce an extended decoupling scheme of the Kondo interaction which allows one to treat the spin fluctuations and the Kondo effect on an equal footing. The calculations, developed in a self-consistent one-loop approximation, lead to the formation of a damped collective mode with a dynamic exponent z=2 in the case of an antiferromagnetic instability. The system displays a quantum-classical crossover at finite temperature depending how the energy of the mode, on the scale of the magnetic correlation length, compares to k_B T. The low temperature behavior, in the different regimes separated by the crossover temperatures, is then discussed for both 2- and 3-dimensional systems.Comment: 24 pages, 5 figures, added reference

Angle Resolved Photo-Emission Spectroscopy signature of the Resonant Excitonic State

We calculate the Angle Resolved PhotoEmission Spectroscopy (ARPES) signature of the Resonant Excitonic State (RES) that was proposed as the Pseudo-Gap state of cuprate superconductors [ArXiv 1510.03038]. This new state can be described as a set of excitonic (particle-hole) patches with an internal checkerboard modulation. Here, we modelize the RES as a charge order with $\bf{2p_{F}}$ wave vectors, where $\bf{2p_{F}}$ is the ordering vector connecting two opposite sides of the Fermi surface. We calculate the spectral weight and the density of states in the RES and we find that our model correctly reproduces the opening of the PG in Bi-2201

Model of Quantum Criticality in He3 bilayers Adsorbed on graphite

Recent experiments on He3 bilayers adsorbed on Graphite have shown striking quantum critical properties at the point where the first layer localizes. We model this system with the Anderson lattice plus inter-layer Coulomb repulsion in two dimensions. Assuming that quantum critical fluctuations come from a vanishing of the effective hybridization, we can reproduce several features of the system, including the apparent occurrence of two quantum critical points (QCP), the variation of the effective mass and coherence temperature with coverage.Comment: 4 pages, 2 figures, new version as published on PRL, journal reference and DOI adde

SU(2)-symmetry in a realistic spin-fermion model for cuprate superconductors

We consider the Pseudo-Gap (PG) state of high-$T_c$ superconductors in form of a composite order parameter fluctuating between 2$p_F$-charge ordering and superconducting (SC) pairing. In the limit of linear dispersion and at the hotspots, both order parameters are related by a SU(2) symmetry and the eight hotspot model of Efetov $\textit{et al.}$ [Nat. Phys. $\bf{9}$, 442 (2013)] is recovered. In the general case however, curvature terms of the dispersion will break this symmetry and the degeneracy between both states is lifted. Taking the full momentum dependence of the order parameter into account, we measure the strength of this SU(2) symmetry breaking over the full Brillouin zone. For realistic dispersion relations including curvature we find generically that the SU(2) symmetry breaking is small and robust to the fermiology and that the symmetric situation is restored in the large paramagnon mass and coupling limit. Comparing the level splitting for different materials we propose a scenario that could account for the competition between the PG and the SC states in the phase diagram of high-$T_c$ superconductors.Comment: 6 pages, 7 figures, published versio